I feel like the only thing stopping it is political taboo. If the U.S. actually supplied tactical nukes for the bay of pigs invasion as planned I think we would see nuke only armies today. As it stands the only time it was used in combat was WWII and no one has ripped the bandaid off diplomatically speaking yet using them in another situation.
with tactical nukes there would be no difference between nuke-only and regular militaries. You can dial down a nuke yield to be equivalent of a 2k lb HE bomb. Now you're right back to a regular military only, now, every bomb is a nuke instead of only a few.
